Patient monitoring systems are commonly used for monitoring the condition of a patient, such as in coronary care units and intensive care units of a hospital. Such systems typically include a bedside monitor having one or more sensors, such as ECG sensors, blood pressure sensors and temperature sensors, attached to the patient. The sensors measure various physiological parameters of the patient. The measured parameters are processed by a system processor. The processed information may be displayed on a video display screen and stored for later analysis. Patient physiological information from several bedside monitors may be forwarded to a central station located, for example, at a nursing station.
The bedside patient monitor and the central station may display physiological parameters as waveforms and/or numerical values. Another important function of patient monitoring systems is to generate alarms when one or more of the physiological parameters indicates that the patient requires attention. Such alarms are necessary because it is not feasible for the display screen of the patient monitoring system to be observed continuously. Alarms are typically annunciated both visibly and audibly.
The conventional way of specifying alarm criteria is to set a fixed upper threshold and a fixed lower threshold for a measurement, such as heart rate. When the measured value goes above the upper threshold or below the lower threshold, an alarm is generated. This approach does not accommodate the situation where a clinician intentionally alters the state of a patient, such as by administering an anesthetic or a drug. Such intervention may cause the patient's heart rate, blood pressure and other physiological parameters to go outside the fixed alarm limits and to generate an alarm, even though these changes are expected and normal. Many clinicians turn off or disable alarms because they become annoyed with a patient monitor that generates an alarm when they intentionally alter a patient's state as described above. When the alarm is turned off, the clinician has the responsibility for monitoring the patient's condition continuously during the intervention process. This may lead to inadequate monitoring. If the clinician resets the alarm limits to the steady state parameter values that are desired after intervention, the patient monitor will generate an alarm immediately, because the parameter values have not yet reached the final values defined by the new alarm limits.
Various, more sophisticated alarm criteria have been proposed. See, for example, J. H. Philip, "Thoughtful Alarms", in J. S. Gravenstein et al, eds. Essential Noninvasive Monitoring in Anesthesia, 1980, page 191-201, and J. H. Philip, "Overview: Creating Practical Alarms for the Future", 1989. Such approaches may be unnecessarily complex for relatively straightforward patient monitoring requirements and do not address alarm detection when a patient's state is intentionally altered.